1. Field of the Invention
The present invention relates to coupling devices for coupling fluid passages of a machine such as a press or injection molding machine.
2. Description of the Prior Art
A coupling device of this type, which is disclosed in Japanese U.M. Patent Application Kokai No. 60-167,888, is shown in FIG. 11. A coupling device 53 attached to a first member 50 is useful for connecting the first bore 54 to the second bore 54' of a second member 55. The coupling device 53 consists Of a body 51 and a valve 52 snugly fitted in the body 51. The body 51 has a large bore 56 communicating with the first bore 54 and a small bore 57 in which the valve 52 slidably fitted. A truncated conical surface 58 between the large bore 56 and the small bore 57 serves as a valve seat.
The valve 52 has a tubular body 70 and a valve head 63 secured to an end wall 73 (with inner and outer surfaces 71 and 72) of the tubular body 70 (with inner and outer surfaces 76 and 77). The valve head 63 is pressed against the valve seat 58 by a compression spring 64 which is provided in the large bore 56. The valve head 63 has a gasket 62 secured to the end wall 73 with a bolt 74. The tubular body 70 has an opening 60 which communicates with the large bore 56 when the valve head 63 leaves the valve seat 58. An axial fluid passage 59 communicating with the opening 60 opens at a front end 75 of the tubular body 70 to form a mouth. An annular elastic gasket 61 is bonded to an annular front surface 78 of the tubular body 70.
In operation, the flow of compressed air from the first bore 54 is blocked in the large bore 56 by the seal made by the valve head 63 and the valve seat 58. When the first member 50 is moved toward the second member 55, the elastic gasket 61 of the valve 52 abuts upon a contact surface 65 of the second member 55. If the force applied to the first member 50 is greater than the sum of the pressure of the compressed air and the push of the compression spring 64, the valve 52 is moved rearwardly with respect to the body 51. Since the gasket 62 of the valve head 52 leaves the valve seat 58, the opening 60 of the tubular body 70 starts to communicate with the large bore 56. As a result, the pressure of compressed air on the valve head 63 disappears, leaving only the push of the compression spring 64.
When the first member 50 is further moved toward the second member 55, the degree of communication between the opening 60 and the large bore 56 increases with the traveling distance of the first member 50. When an edge 66 of the opening 60 reaches the large bore 56, the coupling between the first and second bores 54 and 54' is completed.
When there is no coupling action for a long period of time, the vapor of the compressed air remained in the large bore 56 condenses on the inner surface of the large bore and/or the compression spring 64, forming a considerable amount of "drain" in the large bore 56. An example is a case where the metal mold of a press and external conduits are replaced. The press generally has several extruding cylinders for taking a molding from the metal mold in which air passages to the cylinders are provided. The number of extruding cylinders depends on the type and shape of a molding and thus the metal mold to be replaced. Consequently, the number of coupling devices used for the press should be equal the maximum number of cylinders for the metal mold. When the number of cylinders is small, there are some unused coupling devices, in which drains accumulate. When such coupling devices are used, the drains enter the air passages of the metal mold, eroding the passages, causing clogs and impairing the operation of the extruding cylinders.